In an electrical power device or circuit, a continuous rated current flows in a normal state. If, however, there occurs a problem in the electrical power device or circuit, or if a fault current beyond a tolerance range is flown to the electrical power device or circuit, major components within the electrical power device or circuit may suffer damages due to the fault current.
A current limiting device has been developed to prevent generation of such a fault current. The current limiting device is connected to a track circuit of the electrical power device or circuit and is capable of adjusting an electric current. Particularly, many researches have been actively conducted on a superconducting current limiting device using a superconductor. The super conductor has an electrical resistance substantially close to zero (0) at a very low temperature, and the electrical resistance thereof increases rapidly with a rise of the temperature.
If, however, a fault current over a certain level is applied to the superconducting current limiting device, there is a risk that even the superconducting element is damaged. Further, if the fault current over a certain level is applied, the electrical resistance of the superconducting element may become close to infinity and has adverse influence on devices to which the electric current needs to be applied continuously for normal operations. In view of this problem, there have been conducted many researches upon a method of controlling the fault current by adjusting the number of superconducting elements being operated or a flow path of the electric current based on the magnitude of the fault current, by using a layout of the superconducting elements and a switching element.
In this regard, Korean Patent Publication No. 2011-0002749 (entitled “Method for improvement of recovery characteristics using a trigger of superconductor in a superconducting fault current limiter with magnetic coupling of two coils”) discloses a method of controlling a fault current by improving recovery characteristics of a superconducting current limiter through magnetic coupling of two coils.